1. Field of the Invention
The present invention relates to a power amplifying apparatus, and more particularly, to a power amplifying apparatus applicable to a communication device transmission system and having improved current control performance and a reduction in size and cost as compared to the related art without the need for a separate current mirror circuit for sensing current.
2. Description of the Related Art
Generally, in a radio frequency (RF) block of a mobile communications terminal, a power amplifier is used in order to amplify an RF signal output.
Research into a power amplifier, to which complementary metal oxide semiconductor (CMOS) technology appropriate for the compactness and integration thereof is applied, has been actively conducted. In addition, a power regulator (called a low drop output (LDO)), implemented to be appropriate for the power amplifier, has been developed in order to stably control an operation of the power amplifier. Research into technology for supplying more stable power using the power regulator has been conducted.
The power regulator (LDO) includes a plurality of power PMOS transistors connected in parallel with each other in order to supply current, required in the power amplifier in a sufficient amount.
Each of the plurality of power PMOS transistors supplies a current having a preset level, and the currents supplied through the plurality of individual power PMOS transistors are totaled, whereby the current required in the power amplifier may be supplied.
A stable operation of an analog control block supplying the power to the power amplifier using the power regulator is required.
A power amplifying apparatus according to the related art is configured to include a power regulator supplying a current Id and a voltage Vdd controlled according to an inputted control voltage Vramp and a power amplifier having a power transistor receiving the current and the voltage from the power regulator and amplifying the power of the input signal Sin.
In addition, the power regulator includes a plurality of power PMOS transistors, which are operated at a low source-drain voltage and thus, are operated in a triode region in which a large change in drain current is generated even in the case of a small change in the source-drain voltage, such that a large change in current is generated even in the case of a small change in voltage. Accordingly, under these operation conditions, control of the current should be performed.
In this configuration, in order to accurately control driving currents provided to the power regulator, sensing PMOS transistors, sensing driving currents flowing in the plurality of individual PMOS transistors included in the power regulator, are connected thereto.
The power amplifying apparatus further includes a current mirror circuit mirroring the driving current sensed by the sensing PMOS transistor. The power amplifying apparatus converts the sensed current through the current mirror circuit into voltage, and then controls current bias of the power amplifier based on a voltage difference between the converted voltage and a reference voltage.
However, the power amplifying apparatus according to the related art includes the current mirror circuit, thereby causing increases in both the size and cost thereof.
In addition, since the power amplifying apparatus includes the current mirror circuit, as an electrical length of a passive element included in the power amplifying apparatus becomes elongated, an error is generated between the sensed voltage and the reference voltage, such that the driving current may not be accurately controlled.